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heat shield

Device designed to protect part of a spacecraft from heating, particularly when entering a gaseous atmosphere at high speed. It is made of insulating or ablative material.

Heliocentric (Sun-centred) theory

Theory that places the Sun at the centre of the “world”. It was originally expounded by the Greeks in the 3rd century and taken up later by Copernicus in the 16th century, after which it slowly gained acceptance.